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Gregor MendelGregor MendelGenetics =the

branch of biology that deals with heredity.

A great deal of what we know about genetics began with the work of a monk named Gregor MendelGregor Mendel, who experimented with sweet pea plants in the 1800s. 22

Mendel’s Work

•Mendel studied the patterns of inheritance in pea plants.

•He chose seven traits to follow.

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•Mendel needed to make sure he had plants that always gave the same offspring-called true breeding.

•He “self-pollinated” plants until he got seeds that always gave the same offspring.

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He took a purple flower plant and crossed it with a white flower plant.

He called these the parent generation (P1 generation)

What do you think the offspring (the F1 generation) looked like?

ALL PURPLE

X

Pollen

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POLLEN

SAY SAY

WHAT??????

WHAT??????

??

F1

F266

Mendel concluded:1. Something is being passed

from parent to offspring. 2. Sometimes you can see

“it” and sometimes you can’t.

3. If you can see “it”- “it” is dominant.

4. If “it’s” there and you can’t see “it”- it’s recessive.

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1. Dominant alleles are shown using a capital letter (R)

2. Recessive alleles are shown using a lower case letter (r)

Examples: R=red r=pinkRR - ?Rr - ?Rr- ?Each version is called an allele.

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Alleles are locted on genes on chromosomes.

Law of DominanceLaw of Dominance

States that the dominant allele States that the dominant allele will will preventprevent the recessive the recessive

allele from being expressed. allele from being expressed. The recessive allele will The recessive allele will onlyonly appear when it is paired with appear when it is paired with

another recessive allele in another recessive allele in the offspring.the offspring.

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1111

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We have two copies of all of our chromosomes Why?

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BOY OR GIRL?

                                                                                       

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What is a gene?What is a gene?• A segment on the chromosome A segment on the chromosome

that codes for a protein.that codes for a protein.• People have two copies of each People have two copies of each

gene, one copy inherited from gene, one copy inherited from the the mothermother and the other copy and the other copy inherited from the inherited from the fatherfather. .

• There are many versions of There are many versions of each gene-alleleseach gene-alleles

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If the two alleles in the pair are

identical, then the condition called homozygous.

•

If the 2 alleles are different, the condition is called heterozygous. The term “hybrid” is sometimes used to refer to heterozygous.1616

Genotype: the

genes or alleles

(RR, Rr, rr)

Phenotype: an organisms physical appearance (Red, White)

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How did you end up with the traits and genes that you got?

During meiosis, each egg or sperm only gets one copy of each chromosome.

Law of Segregation (separation) states that gene pairs separate when gametes (sex cells) are formed, so each gamete has only one allele of each gene pair.

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A

b

a

B

A

b

a

B

A

b

a

B

A

b

a

B

A

b

a

B

Law of Law of Independent Independent AssortmentAssortment states that

different pairs of genes separate

independently of each other

when gametes are formed.

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Example:

Just because you get the gene for brown hair does not mean you will get the gene for blue eyes.

REVIEWREVIEW1. A trait is a characteristic an individual receives

from its parents. 2. Genes carry the instructions responsible for the

expression of traits. 3. A pair of inherited genes controls a trait. 4. One member of the pair comes from each

parent.5. Alternative versions of genes are known as

alleles.

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REVIEWMendel’s Principles of Inheritance

• Inherited traits are transmitted by genes which occur in alternate forms called alleles

1. Principle of Dominance - when 2 forms of the same gene are present the dominant allele is expressed

2. Principle of Segregation - in meiosis two alleles separate so that each gamete receives only one form of the gene

3. Principle of Independent Assortment - each trait is inherited independent of other traits (chance)

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Punnett Squares• Used to determine the probability

of a combination of alleles• Example: If a heterozygous black

rabbit is crossed with a heterozygous black rabbit, what are the chances the offspring will be black?

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B=Black

b= Brown

Genotypes?

Phenotypes?

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Example EOCT Question:Example EOCT Question:Earlobe shape is a human trait. Some people have free earlobes while others

have attached earlobes. Two parents with free earlobes have four children. Three

children have free earlobes and one child has attached earlobes. If these parents

have another child, what is the probability that the child will have attached earlobes?

A 25%

B 50%

C 75%

D 100% 2626

Example EOCT question:

In humans, a widow’s peak is dominant over a continuous hairline. Mary’s father has a widow’s peak, but Mary and her mother have a continuous hairline. What is the genotype of Mary’s father?

A HHB HhC hh D cannot be determined

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Incomplete dominance

- cross between

organisms with two

different phenotypes that

produces offspring with a

third phenotype that is a

blendingblending of the parental

traits.

Ex. Red and White = Pink 2299

Incomplete Dominance

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CodominanceCodominance• a cross between organisms with two different phenotypes

produces offspring with a third phenotype in which both of the

parental traits appear together. 

• Ex: Yellow and Orange = yellow with orange spots

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CodominanceCodominance•Both

phenotypes are expressed at the same time.

•Example: Blood

Types

Genotype Phenotype

IOIO Type O

IAIO Type A

IAIA Type A

IBIO Type B

IBIB Type B

IAIB Type AB

There are 3 alleles for blood type- multiple alleles

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CodominanceR = allele for red flowers

W = allele for white flowers W = allele for white flowers red x white ---> red & white spotted

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Polygenic traitsMost traits are controlled by many

genes, not just one.Examples: hair color and skin color.

There are several genes that control them.

This is the reason that there are so many different colors of hair and

skin in humans.

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Sex Linked TraitsTraits associated with

particular sexes are called sex-linked or X-linked traits. These are usually carried on

the X chromosome. Females = XX

Males = XY

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KaryotypKaryotyp

ee

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1st 22 are Autosomes, the last pair (XY) are sex chromosomes)

Charts that show relationships within a

family

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Pedigr

ee

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Autosomal-Dominant

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SEX-LINKED

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SEX-LINKED

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Autosomal -Dominant

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Genetic

Disorders

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Huntington’s Disease

• Huntington's disease degenerative disease that causes certain nerve cells in your brain to waste away.

• you may experience uncontrolled movements, emotional disturbances and mental deterioration.

• The disorder was documented in 1872 by American physician George Huntington.

• Fatal----ages:30-60

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Colorblindness

•Sex-linked trait• Gene for color vision located on

the X chromosomes.• MalesMales are more likely to have

colorblindness because they have only one X chromosome

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What do you see?

The individual with normal color vision will see a 5 revealed in the dot pattern. An individual

with Red/Green (the most common) color blindness will see a 2 revealed in the dots.

What What

do do

you you

see?see?

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TEST

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Down SyndromeDown Syndrome• Three copies of chromosome #21.

• Symptoms: mental retardation and some physical deformities

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Down’s Syndrome – How do you get 3 copies of chromosome 21?

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Nondisjunction – failure of chromosomes to separate properly during cell division

Cystic Fibrosis• caused by a recessive

allele on chromosome #7.

• Deletion of three bases.

• Affects the body's respiratory and digestive systems.

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HemophiliaSex-liked,

recessive

trait

Located on

the X

chromosome

Missing a

protein

necessary

for blood

clotting

Can bleed

to death

from minor

cuts.

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Queen Victoria’s Pedigree showing Hemophelia

Sickle Cell

People who carry the tendency to have sickle cell anemia are less likely to die from malaria.

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Gene Therapy

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The insertion of healthy genes into an individual’s cells or tissues to treat a disease.

Example EOCT question:Example EOCT question:

What is nondisjunction?

A. failure of chromosomes to separate during meiosis

B. failure of the cytoplasm to divide properly

C. the insertion of a gene into a different chromosome

D. the deletion of a gene from a chromosome

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Which of the following shows how information is

transformed to make a protein?

A DNA RNA proteinB gene chromosome proteinC cell respiration ATP proteinD ATP amino acid protein

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Information on mRNA is Information on mRNA is used to make a sequence used to make a sequence

of amino acids into a of amino acids into a protein by which of the protein by which of the

following processes?following processes?A replicationB translationC transcriptionD transference

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Pea plants have seeds that are either round or wrinkled. In this cross, what will be thephenotypic ratio of the offspring?

A 50% RR and 50% RrB 25% RR, 50% Rr, and 25% rrC 50% round seeds and 50% wrinkled seedsD 100% round seeds

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What is a source of genetic variation?A mutationB adaptationC replicationD transcription

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A homozygous traitB dominant traitC recessive traitD heterozygous trait

In Mendel’s experiments with a single trait, the

trait that disappeared in the first generation

and reappeared in the next generation is called

the

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